I've started taping brushes together in various sizes. It allows me to quickly switch brushes, plus the added length gives me some room to step back from the canvas, increasing my reach. I spoke with Rosemary Brushes about manufacturing such a brush. They call a double-ended brush a "kayak", but have a very limited capacity to make them, mostly in the small sizes. The bulk purchase of brush stock, especially the handles, makes it difficult to create a new style of brush. They purchase handles in bundles, like a thousand units. So, I'll keep using tape.